“Pixel depth” refers to the number of tones a pixel can display, determined by the bits used to display the pixel. One bit can contain one color (black), four bits can contain any combination of the binary numbers 1 and 0, so 16 shades are possible (0000, 0001, 0011, 0010, etc.). Photoshop works with 8, 16 and 32-bit images. In 32-bit images, only 24 bits are available (the others are reserved for masking and other functions) but each pixel can still produce 16.7 million colors.